The vegetable, when taken in the form of salad or eaten cold, could help reduce levels of white blood cells, which are produced when the body is challenged.

Eating potatoes is not only good for bowel health, but also for the whole immune system, especially when they come in the form of a potato salad or eaten cold.

In a study on an animal model, researchers in Spain found that pigs fed large quantities of raw potato starch (RPS) not only had a healthier bowel, but also decreased levels of white blood cells, such as leucocytes and lymphocytes in their blood.

White blood cells are produced as a result of inflammation or disease, generally when the body is challenged.

The general down-regulation of leucocytes observed by the Spanish researchers suggests an overall beneficial effect, a generally more healthy body.

The reduction in leucocyte levels was about 15 percent. Lower lymphocyte levels are also indicative of reduced levels of inflammation, but the observed reduction in both lymphocyte density and lymphocyte apoptosis is surprising.

In what was the longest study of its kind, pigs were fed RPS over 14 weeks to find out he effect of starch on bowel health

“The use of raw potato starch in this experiment is designed to simulate the effects of a diet high in resistant starch,” said study leader Jose Francisco Perez at the Universitat Autonoma de Barcelona, Spain.

Humans do not eat raw potatoes, but they do eat a lot of foods that contain resistant starch, such as cold boiled potatoes, legumes, grains, green bananas, pasta and cereals. About 10 per cent of the starch eaten by human is resistant starch - starch that is not digested in the small intestine and so is shunted into the large intestine where it ferments.

Starch consumption is thought to reduce the risk of large bowel cancer and may also have an effect on irritable bowel syndrome (IBS).

Immunology expert Lena Ohman’s team previously found that the overall lymphocyte levels do not vary for IBS patients, but that lymphocytes are transferred from the peripheral blood to the gut, which support the hypothesis of IBS being at least partially an inflammatory disorder.

She says the decrease in lymphocytes observed by the Spanish is therefore interesting and a diet of resistant starch may be worth trying in IBS patients.

Ohman is currently at the Department of Internal Medicine, Goteborg University, Sweden. The study is published in the journal Chemistry and Industry, the magazine of the SCI.